1. Field of the Invention
The present invention relates to a sheet feeding device that pneumatically float sheets to be picked up one by one from a sheet stack, and also relates to an image forming apparatus including the sheet feeding device.
2. Description of Related Art
Some image forming apparatuses include sheet feeding devices as described above, in order to feed sheets (e.g., paper) to imaging units (e.g., see Japanese Patent Laid-Open Publication No. 2010-254462). The sheet feeding device 100 disclosed in Japanese Patent Laid-Open Publication No. 2010-254462, will be described in detail below with reference to FIG. 13.
The sheet feeding device 100 includes a blowing device 102 that blows air toward the top edge of a stack of sheets S (on the positive side in the z-axis direction), thereby floating the top sheet S1. Endless suction belts 104 with a number of through-holes provided therein are disposed above the stack of sheets S. By means of an internal fan provided in a chamber (not shown) positioned inside relative to the suction belts 104, the top sheet S1 is attracted to the suction belts 104 by drawing air between the stack of sheets S and the suction belts 104 into the chamber via the through-holes. The suction belts 104 are rotated by a drive force from a motor (not shown). Accordingly, the attracted sheet is carried in the x-axis direction to a receiving port 108 of a transportation path 106. Thereafter, the top sheet S1 is carried through the transportation path 106 to an imaging unit (not shown).
The sheet feeding device 100 further includes an image pickup device 110 and a control circuit 112. The image pickup device 110 captures images of the floated top sheet S1 and another sheet immediately therebelow, from a predetermined distance in the y-axis direction relative to one side P1 of the stack of sheets S. The control circuit 112 calculates the gap between the sheets on the basis of the images captured by the image pickup device 110. Moreover, the control circuit 112 adjusts the volume of air from the blowing device 102 on the basis of the calculated gap between the sheets.
However, in the case of the configuration in FIG. 13, when viewed in a plan view in the z-axis direction, a sheet edge portion near the side P1 might be distanced significantly from the edge of the suction belt 104 on the positive side in the y-axis direction. In such a case, the sheet is not attracted sufficiently to the suction belt 104, so that the sheet edge portion near the side P1 hangs downward. As a result of the edge portion hanging downward, an image of the top sheet S1 is captured with the edge portion near the side P1 overlapping with the sheet therebelow. Accordingly, the control circuit 112 fails to calculate the gap between the sheets accurately.